Generally, the excessive use of groundwater in a coastal area lowers a water level of the groundwater, thus causing salt water (sea water) to flow into the groundwater and thereby contaminating the groundwater. Consequently, the groundwater cannot be used as drinking water, agricultural water, or industrial water.
Accordingly, a groundwater observation system is used in coastal areas, in which a groundwater observation well is bored and a wired or wireless measuring sensor is installed in the observation well to measure a groundwater level, temperature, electrical conductivity values, the position of a fresh water-salt water interface and the like, so as to monitor changes in groundwater.
Here, since the position of the fresh water-salt water interface (the interface between fresh water and salt water of the groundwater) is frequently changed by various complex phenomena such as the excessive pumping operation of the groundwater, rain, a tide phenomenon, and a sea level rise due to global warming, apparatuses capable of precisely tracking a changed position are being developed.
Meanwhile, the measuring sensor provided in the groundwater observation well of an actual coastal area is installed at a fixed depth regardless of whether it is a wired or wireless sensor, so it is difficult to check the position of the fresh water-salt water interface in real time. Further, when an apparatus for tracking a salt-water surface of the groundwater is inserted into or removed from the groundwater observation well, it is difficult to precisely install or remove a recovery apparatus at or from the groundwater salt-water-surface tracking apparatus according to a diameter of the observation well.
Further, when one desires to adjust buoyancy in order to precisely position the groundwater salt-water-surface tracking apparatus at the interface between the fresh water and the salt water of the groundwater, a water tank having the same concentration as the salt water is prepared and then gravity is adjusted. However, there is difficulty in adjusting the concentration in this method, and in addition, gravity adjustment is required per water tank, so that it is inconvenient.
As the related art of the present invention, an apparatus for tracking a position of a fresh water-salt water interface is proposed in Korean Patent Publication No. 10-0977155.
As shown in FIG. 1, the conventional apparatus includes a buoyancy deriver 10, a wireless measuring sensor 20, and a perforated pipe 30. The buoyancy deriver 10 is in the shape of a pipe having a space therein, and is closed at a bottom thereof, with a separable closing cap 14 mounted to a top thereof. Further, a bracket 12 having a through hole 12a is formed in a central portion of the bottom of the buoyancy deriver 10, and a metal 15 is provided in the closing cap 14 to be attached to a magnetic material. The buoyancy deriver 10 adjusts an amount of distilled water accommodated in the internal space to adjust buoyancy. The wireless measuring sensor 20 is mounted to the bottom of the buoyancy deriver 10. The perforated pipe 30 is mounted to the bottom of the buoyancy deriver 10 to surround the wireless measuring sensor 20.
Such a conventional apparatus is configured to be put into or discharged from an observation well while being secured to an electromagnet of a retractor (not shown) by the metal 15 provided in the cap 14, and is moved up and down in a longitudinal direction of the observation well according to a water level of the fresh water-salt water interface, thus indicating a position.
In this regard, as a groundwater inlet port is longitudinally formed through the observation well, it receives underground groundwater through the groundwater inlet port.
However, the conventional buoyancy deriver 10 is problematic in that an upper end or a lower end is caught by the inlet port of the observation well while the deriver moves up and down along the observation well, so that it may not provide exact information on position.